Good point by P East, what about the plumbing?
Yes, your inspector cannot see what is in the ground so I have seen some builder's plumbers water test before they get too far but most don't and testing should be mandatory.
Nevertheless, you inspector should check for any obvious damage, number and position of pipes coming through slab as well as termite protection and many many other things not related to plumbing.
The fact is that unless you have someone on the site all the time, you cannot check and control everything, so there are going to be blind spots. Stage inspections are merely best attempt(from experience) at a sweet point between price and value which nevertheless will still leave owner with some risk. No inspections? Much higher risk.
Another blind spot is pre-plaster inspection, it is not mandatory under building regulations but who will check that your perfectly good building elements have not been damaged by subsequent trades, who will check integrity of fire separation walls in units? Who will check that your walls are straight? Who will check that previously reported framing defects have been fixed? and many other things.
Finally, building surveyor's may (and do) rely on certificates, so regularly despite insulation certificates I find insulation a thermal leaking bucket in majority of homes, see below: